Brazing is one of many ways frequently used to bond metal objects together. According to this bonding method, brazing powder is placed at the connection point between the two objects and they are heated until the brazing powder melts which in turn bonds the objects together. Particularly in the aerospace industry, this is used to assemble various parts of a jet engine.
Using brazing powders is particularly difficult and inefficient. Getting the brazing powder in position, in the right quantities evenly distributed is difficult. Maintaining it in position is also difficult.
There are composite products which are the braze powders held together by binding material. Vitta Corporation sells such a product. But the product is relatively rigid and requires special forming tools that are very expensive. Due to the nature of the product, it is very difficult to use. Other binders are unsuitable because they leave ash behind on the surface which interferes with the bonding or corrode the treated metal surface.
In many applications, a braze slurry is required. Braze slurries are powdered brazing alloys held together as a paste by one of several well known organic binding system. When superalloys are brazed together, a metal oxide can form at the braze surface. This is particularly a problem with superalloys formed from aluminum, titanium, hafnium, and chromium. When these are heated above 800.degree. F. even a trace of oxygen in the braze furnace can form an oxide with these metals. This can prevent adequate bonding of the surfaces.
To prevent this, the parts are frequently nickel coated to prevent oxide formation. Nickel coating is undesirable because it is an expensive additional step. It can require not only coating of the selected area, but also masking of other areas to avoid nickel plating on other surfaces.